Slate Belt municipalities would face reduced financial risk under a revised proposal for solid-waste disposal outlined at a special meeting of the Lower Mount Bethel Township supervisors last night.

Nolan Perin of Grand Central Sanitation, Plainfield Township, said another county is interested in sending 250 tons of solid waste per day to the 500- ton-per-day capacity resource recovery facility GCS has offered to build. Perin has said the 10 Slate Belt communities would generate about 100 tons per day. The remainder of the plant's capacity would be sold to commercial users.

At a meeting last month, Perin and Gerard Jacobs of Russell, Rea and Zappala, investment bankers of Pittsburgh, had explained their proposal would have the municipalities serve as the ultimate credit support for financing the project. The county, which Perin did not name last night, would share that risk and reduce the municipalities' exposure in the event of such circumstances as a natural disaster destroying the facility, changing environmental regulations, drying up of the commercialwaste stream, unforeseen increases in insurance costs or bankruptcy by the utility purchasing the power from the plant.

The supervisors called last night's meeting to receive more information about several waste disposal alternatives under review.

Recapping the highlights of the GCS plan, Perin noted the firm would solicit bids from several blue-chip vendors to build the privately owned incinerator. Municipalities would initially pay a $30 per ton tipping fee that would escalate according to a mutually agreed upon index over a 20-year contract.

However, the GCS proposal would provide for profits from operation of the facility to be shared with sponsoring municipalities. He said, "I don't anticipate distribution of those profits until the debt is paid." Although Perin said profits could be shared by the firm and municipalities sooner, he indicated, "We don't believe that's good business. We'd like to see the debt paid first." Last month, Jacobs said construction of the $40-million facility would require an estimated $70-million bond issue.

How quickly the debt could be reduced, Perin said, would depend on his success in selling the remaining capacity to commercial users at substantially higher rates than those charged to the sponsoring municipalities. If market conditions hold, he said, the debt probably could be retired in about five or six years.

He cautioned that, although a few solid waste disposal facilities now exist for the many sources of waste, the approval and construction of one or two landfills in the state could change the situation.

Another benefit of selling initially excess capacity to commercial users, Perin said, would be that commercial contracts would be staggered in term and would be of shorter duration - from one to five years. That would mean that as municipalities grow, GCS could reduce outside commercial tonnage to accommodate increased municipal needs.

Collection, he said, is an issue to be addressed separately from disposal.

He said he hopes to contact John Molnar, solicitor for Bangor Borough Authority, which has hosted the Slate Belt solid waste meetings, to arrange a time, hopefully in early April, to present computer cost runs and profit projections for the entire 20-year contract term. He said he will present "several different scenarios" at that time.

Also addressing the supervisors last night was Allen O'Dell of the Joint Planning Commission of Lehigh-Northampton Counties. Outlining the resource recovery proposal of the Lehigh Valley Solid Waste Authority, O'Dell said the authority is currently negotiating a contract with American Ref-Fuel, a private company that would design, construct, own and operate the 1,000-ton- per-day facility to be built on authority-owned land in Lower Saucon Township.

O'Dell said the authority has received approval to issue $100 million in tax-free bonds to finance the project. The approval was granted by the Pennsylvania Department of Commerce for 1986.

He said the authority will probably be ready to present a 20-year contract proposal to interested municipalities sometime in May and will seek a response by about August. The municipalities, either individually or collectively, will be required to guarantee a minimum tonnage to the plant. They will be allowed to exceed that minimum by about 20 percent, he said.

O'Dell said, "I've suggested they (the authority) look at some kind of collective approach." He said that way, communities that don't meet their individual commitments will not be penalized unless the participants as a whole are short of the minimum tonnage. O'Dell said to provide for growth, the vendor has offered to build a 300,000-ton-per-year facility. The authority could commit to 200,000 tons initially and purchase added tonnage later. In the meantime, the excess capacity would be sold to other users.

O'Dell advised all municipalities interested in the Lehigh Valley proposal to pass ordinances authorizing them to direct their waste to a specific facility and to contract with licensed haulers. That step, he said, is not binding. "At this point, I have recommended all the municipalities adopt the ordinance to continue to be eligible," he said.

Supervisors' Chairman Frank Bilotta said Lower Mount Bethel held last night's meeting to receive added information about the options facing the municipality. He said he was advised Bangor Borough Authority did not have any new information to present about the Bangor Borough Incinerator at present. Bilotta said Bangor officials were invited to attend the meeting anyway, even if just to listen.